Semiconductor image sensors are operated to sense light. Typically, the semiconductor image sensors include complementary metal-oxide-semiconductor (CMOS) image sensors (CIS) or charge-coupled device (CCD) sensors, which are widely used in various applications such as digital still camera (DSC), mobile phone camera, digital video (DV) and digital video recorder (DVR) applications. These semiconductor image sensors utilize an array of image sensor elements, each image sensor element including a photodiode and other elements, to absorb light and convert the sensed light into digital data or electrical signals.
A back side illuminated (BSI) CMOS image sensor is one type of CMOS image sensors. The BSI CMOS image sensor is operable to detect light projected onto its backside. The BSI CMOS image sensor can shorten optical paths and increase a fill factor to improve light sensitivity per unit area and quantum efficiency, and can reduce crosstalk and photo response non-uniformity. Hence, the image quality of the CMOS image sensor can be significantly improved. Furthermore, the BSI CMOS image sensor has a high chief ray angle, which allows a smaller lens height to be implemented, so that thinner camera modules are achieved. Accordingly, the BSI CMOS image sensor technology is becoming a mainstream technology.